This invention relates to a shadow mask for a flat faced cathode ray tube (CRT) for color display, and more particularly relates to such a mask having a border pattern.
Cathode ray tubes for color television and allied display applications typically employ a shadow mask to shadow (spatially filter) the electron beams coming from the three electron guns mounted in the neck of the tube, such that each beam excites only one color of a three-color phosphor display screen disposed on the internal surface of the face of the tube. This shadowing is accomplished by providing an array of apertures in the mask corresponding to an array of phosphor elements in the screen.
Conventional CRT faces are curved. Currently, two-dimensional (cylindrical) or three-dimensional (quasi-spherical) curvatures are employed. Although CRTs have recently been developed which have faces with reduced curvatures, it would be desirable for a number of reasons, including aesthetic appearance, reduced ambient light reflections and fabrication costs, to have a CRT with a face with no curvature at all.
A flat-faced CRT is currently being developed in which the shadow mask is tensioned behind the flat display surface, much like a drum skin, to provide structural rigidity and to overcome thermal distortion problems during operation. A uniform stress distribution in this mask is desirable since this allows the use of higher tensioning stresses which further improves the structural and thermal behavior. Such tensioning stresses could be as high as 60 to 80% of the yield stress of the mask material.
Additional advantages in tube design and cost of automation could be realized if a "non-married" fabrication process could be used, that is, the shadow mask and phosphor patterns are produced independently, rather than dependently as is the present practice for conventional color CRTs. To achieve such a "non-married" fabrication process, the accuracy of aperture and phosphor element placement within 5 to 10 microns must be uniformly achievable.
U.S. Pat. No. 3,500,100 relates to a character display tube having a mask with a compliant area surrounding an indicia area to minimize distortion of the indicia area. This concept is inappropriate for use with a tensioned mask in a flat-faced color CRT, since it would keep the central viewing area of the mask essentially stress free.